Center bolt type acoustic transducer

ABSTRACT

A center bolt type of acoustic transducer has means for mounting such transducer at the nodal plane. This means includes a flange integral with a transducer part and rigid clamping rings cooperating with such flange but acoustically isolated therefrom by suitable gaskets for support. The nodal plane is located at the flange.

v United States Patent 1191 1111 3,772,538 Supitilov Nov. 13, 1973CENTER BOLT TYPE ACOUSTIC [56] References Cited TRANSDUCER UNITED STATESPATENTS [75] Inventor: Michael C. Supitilov, St. Charles, Ill. 3,328,6106/1967 Jacke 310/83 3,368,086 2/1968 Libby 310/8.7 X [73] Asslgnee- 3Kane Charles 3,394,274 7/1968 Jacke et al 31o/s.7 x

[22] Filed: Jan. 8, 1973 Primary Examiner-J. D. Miller AssistantExaminer-Mark O. Budd [21] Appl' 321976 Attorney-Robert L. Kahn RelatedUS. Application Data [63] Continuation of Set. No. 199,892, Nov. 18,1971, ABSTRACT abandoned' wh'ch a communion of 9" A center bolt type ofacoustic transducer has means May 1970' abandm'ed' for mounting suchtransducer at the nodal plane. This I means includes a flange integralwith a transducer part 521 U.S. Cl. 310/91, 310/8.2,8.7 and rigidclamping rings cooperating with such flange Int. but acous ical y isoate he o suitable gaskets of Search for pp The nodal plane is located atthe flange.

5 Claims, 8 Drawing Figures PAIENTEUnnv 13 I975 FIG. 8

Inventor MICHAEL C. SUPITILOV.

JPM x/am/ ATTY CENTER BOLT TYPE ACOUSTIC TRANSDUCER to merely asceramics," but understood to have piezo properties. The assembly ismaintained in preset compression by an axial bolt. Such an assembly isgenerally operated at a suitable frequency (as an example, about 20,000Hz) for accomplishing various objectives.

Transducers of this general type have problems in connection withinterfaces between physically separate parts of a transducer and also inconnection with supporting the unit. In addition, such transducers arenot susceptible to adaption for various jobs requiring tool changewithout factory adjustment or redesign. In many instances priortransducers are not adaptable for operating in parallel as part of abattery of transducers without substantial spacing between adjacenttransducers. Such spacing is due to mounting requirements of eachtransducer.

An additional disadvantage of some prior transducers is the inability tochange the number of the vibration transmitting half-wave lengths at thefront slug (or horn) as may be necessary to apply acoustic energy to adesired work region. A substantial drawback in prior transducers is thenumber of separate parts (and thus the number of interfaces) required ina transducer unit maintained in preset compression by the axial boltmeans. This last named drawback may result in reduced efficiency anddefinitely in increased manufacturing cost. Opposed faces of separatephysical parts of a transducer unit, maintained in compression, must befinished toabout one ten thousandth of an inch and in- A transducerembodying the present invention has definite advantages over priortransducers. The new transducer has minimum number of interfacesrequiring preparation of opposing surfaces; the entire transducerassembly, preset for predetermined piezo ceramic compression need not bedisturbed when making a tool change at the work. end thereof; thestationary transducer support means is statically independent of staticceramic compression forces; the new transducer permits close spacingbetween separate parallel transducers and thus permits transducers tooperate within minimum space.

A transducer embodying the present invention comprises a high potentialflat electrode plate of substantial thickness having flat ceramic platesdisposed on opposite sides of the electrode. A rear slug is disposedagainst one face of a ceramic and a front slug (or horn as required) isdisposed against the outer face of the remaining ceramic. A bolt extendsaxially through the assembly and is pretensioned by internally threadedportions to subject the ceramics to a predetermined operatingcompression.

For convenience, round ceramic discs are used. The same circularconfiguration is also used for the elements of an assembly. Except forthe ceramics which should not project beyond the metal portions, theouter diameters of the ceramics, electrode plate and rear slug may bethe same. The front slug (or horn) will have a circular outer shape, atleast at the rear portion thereof. The outer diameter of the front slugat the rear portion thereof will be somewhat greater than that of theadjacent ceramic due to the presence of a mounting flange extendingradially from the slug exterior. Otherwise the forward slug (or horn)will have a shape and/or dimensions dictated by engineeringconsiderations. The

mounting flange is part of a stationary mount structure.

The mount structure for a transducer provides a highly efficient andeffective support means. The transducer mount is such that the staticweight or load pressure of a transducer unit will not result in anychange of pre-compression upon the ceramics, thus isolating the staticpreset force of compression on the ceramics from the mounting of atransducer with relation to work. The annular support flange for atransducer projects laterally beyond the remaining peripheral parts ofthe transducer. The extent of support flange projection is quite smallso that the entire transducer has minimum requirements for mountingspace.

The new transducer has its vibratory output longitudinally of thetransducer assembly. The nodal plane is normal to the transducer axis atthe annular flange and has minimum vibratory amplitude. Longitudinallyin either direction from the'nodal plane the amplitude of longitudinalvibration increases to a maximum along the transducer axis at a regionone-fourth of a wave length away from the nodal plane and thereafterdecreases further away from the first nodal plane until one-fourth of awave length from the maximum or peak amplitude there is a new nodalplane. As a rule, a transducer generally extends only for one-fourthwave length to the non-working rear end thereof. The front (working)portion is dimensioned to be some desirable number of odd one-fourthwave lengths from the center of the nodal flange.

In the new transducer, the nodal plane is located near the rear of theforward slug (or horn). In this new construction, the front slug (orhorn) is always somewhat longer than one-fourth wave length (or oddmultiple thereof).

The location of the nodal plane forwardly of the ceramic assembly has anumber of advantages. The design of the transducer mount structure isquite flexible and lends itself to accommodating various shapes oftransducer housings. The housing may be designed to provide protectionfor high and ground potential leads; to insure adequate dissipation ofheat; to support the housing and transducer in desired relation to thework; and in general to isolate the static load on the work from thestatic load on the ceramics.

A transducer assembly inherently has interfaces between dissimilar solidmaterials having different acoustic impedances. Vibratory energytravelling along a path through one solid medium and encountering adifferent solid medium invariably suffers a transmission loss in theform of backwardly reflected waves. In a homogeneous solid medium, theinterlinking of crystals makes for minimum transmission losses. However,where the nature of a solid medium changes, as between ceramic andmetal, or between two different metals, then the effectiveness of energytransmission will depend upon the relative complex acoustic impedancesof the materials and how intimately the solid materials on oppositesides of an interface can be in physical contact with each other. Thesmoother and flatter the opposed faces are, the less air space therewill be between the two solids. 100 percent is a theoretical ideal whichcannot be attained. Careful surface preparation can come close to theideal so that transmission of wave energy through an interface may reacha value of the order of about 90 or 95 percent. Grease couplants aresometimes used. It is obvious that successive interfaces in a wavetransmission path can rapidly cut down overall transmission efficiency,especially if the facing surfaces are not smooth and flat.

A ceramic disc is available with a very thin silver coating on each faceoriginally put on for poling purposes during manufacturing. The face isusually smooth and true to about a few tenths of a thousandth of aninch. The bond between silver and ceramic is good enough so that thesilver coating may be retained.

Practical considerations dictate the use of a high potential electrodehaving substantial thickness. The new transducer embodying the presentinvention has a minimum number of interfaces. These interfaces are onboth sides of each of two ceramic discs. Having a high potentialrelatively thick metal electrode disc minimizes some lead assemblyproblems for applying potential to the ceramics.

The new transducer assembly in general includes forward and rear slugsbetween which is disposed the ceramic containing portion of theassembly. This portion comprises two ceramic discs properly poled andhaving a common high potential electrode between them. Axially withinthe slugs, ceramic discs and intervening electrode is a bolt formaintaining the transducer assembly at a predetermined compression. Thebolt referred to is frequently designated as a cap screw, but forconvenience, the word bolt will be used herein.

The rear slug (which may be of a suitable solid) is preferably of steelor other dense metal and with the ceramics and high potential electrodeextends for somewhat less than one-fourth wave length at the desiredoperating frequency. The nodal palne is theoretically established nearthe rear end of, but within, the forward slug, ideally the center planeof flange thickness. It is understood that the total physical length ofthe parts will depend on the frequency at which the transducer is to beoperated. In the new transducer, while structural details are notdependent upon any particular frequency, where appropriate the specificfigures or discussion will be in connection with a system for operationat or about twenty thousand cycles per second (KHz). The ceramics may bediscs having athickness of the order of about one-fourth inch, the outerdiameter substantially 1% inches with an axial hole therethrough havinga diameter of about one-half inch for accommodating a compression bolt.The rear slug is cylindrical and has its outer diameter equal to that ofthe ceramics. The front slug is of suitable matter, as titanium or highstrength aluminum, and may be cylindrical or, except for the rearportion, noncylindrical, depending upon engineering considerations. Asis well known in this art, from the rear face of the forward slug theforward working slug (or horn) may vary toward the working or tool endin cross sectional area and shape, as exponential, catenoidal, lin

ear, etc., horn profiles, all well known and fully set forth inpublished literature, to provide desired operating characteristics atthe tool end.

The ceramic material may be anyone of a number of materials well knownin the art and available on the market. Presently, ceramic materials areof barium titanate, lead zirconate titanate and other related compounds.These materials are desirable because they can withstand moderately hightemperatures; have suitable electrical properties; are available atrelatively low cost and have acceptable mechanical properties. As arule, ceramics can withstand considerable compression forces but areweak in tension. Thus, any force tending to bend a ceramic plate (due,for example, to improper matching of faces of ceramic and metal) willresult in fracture of a ceramic plate.

In considering the assembly of high potential electrode, ceramics andslugs, maintained in predetermined compression by an axial bolt, theterm rear slug or resonator may be used to describe a cylindricalmember. Forwardly of the ceramic plates, the member may be designated asa front slug or resonator or horn depending upon its function.Generally, slug or resonator are frequently used interchangeably wherethe member has a generally cylindrical shape and a constant outerdiameter. The same is true of the rear slug or resonator. However,unlike the rear slug or resonator, the forward functioning member maynot only have a wave transmission function, but also a wave amplitudefunction in which case such member is usually designated as a horn.

Where forwardly of the ceramic array it is necessary to have a longenergy path to the tool tip (as in working inside of long pipes),additional multiples of half wave may be provided bolted together toextend the energy conducting path by an integral number of additionalhalf waves. The tool slug (or horn) will be at the end. Path extendingslugs may be cylindrical with all amplitude transforming functionsconcentrated in the end working horn carrying the tool or there may beimpedance transforming sections. The slugs on both ceramic faces areprovided with axial passages or recesses for accommodating a bolt formaintaining an assembly in compressed condition.

In accordance with the invention, an improved supporting means at anodal plane is provided. The nature and location of means supporting atransducer assembly is important because this may represent a drain ofacoustic power from the transducer.

The invention will now be described in connection with the drawingswherein FIG. 1 is a view in section for the most part with certain partsbeing shown in elevation of a transducer unit embodying presentinvention, the unit being mounted in a housing, the transducer unitbeing provided with a tapering horn, shown in section, and a front slug,as a modification, shown in dotted lines.

FIG. 2 is a side elevation of a mounting ring for the transducer.

FIG. 3 is a view on line 3-3 of FIG. 2 showing two mounting rings for atransducer.

FIG. 4 is an enlarged detail of the mounting rings and gaskets.

FIG. 5 is an elevation of a front horn having a modified gasket support.

FIG. 6 is an enlarged detail illustrating the modified gasket support ofFIG. 5 in an assembled transducer.

FIG. 7 is a detail of an outwardly tapering horn which may be used withthe new transducer.

FIG. 8 is an exploded view showing a two piece clamping ring for usewith the general horn arrangement illustrated in FIG. 7, the rings beingshown in exaggerated form to illustrate the mechanical construction.

Referring to the drawings, the transducer includes back or rear slug 10having flat end faces 11 and 12. Slug 10 preferably is cylindrical withaxial bore 14 and counter-bore portion 15. The counter-bore extends fromfree end face 11 for a part of the slug length to internal flat annularshoulder 16. The location of shoulder 16 with respect to the slug lengthis not critical for general applications and it may be located abouttwothirds of way between slug end faces 11 and 12, as shown. Thelongitudinal location of shoulder 16 will be determined in substantialmeasure by acoustic and mechanical considerations including the lengthof the compression bolt to be used, its diameter, modulus of elasticity,strength, etc. The radial dimension of shoulder 16 will be determined bymechanical engineering requirements including clearance for the size ofthe bolt head, or for washer diameters if used. The diameter of bore 14will be determined by the diameter of the bolt shank or for otherdesired clearances while the outer diameter of slut 10 will bedetermined by the outer diameter of the ceramic discs.

In cases where a transducer is required having high vibrating amplitudesat the forward face and broadband (low Q) resonance characteristics,then the choice of backslug material is important. In such cases, thebackslug material should have a high acoustic impedance as compared tothe forward slug. As is well known in the art, this material impedancedepends on a large degree on its density and velocity of propagation.End face 11 and the outer surface of rear slug 10 require no specialfinish other than rust protection. The same is true of the surfaces ofbore 14 and counterbore 15. Shoulder 16 however should be finished to asmooth flat surface perpendicular to the slug axis and accurate to aboutone thousandth of an inch.

Slug end face '12 which abuts a ceramic face must be carefully prepared.The faces of ceramics should be flat to within one or two tenthousandths of an inch and must be truly normal to the axis of theceramic discs. End face 12 of slug 10 must also be perpendicular to theaxis of slug 10 and must also be true to the same degree as the ceramicface. The surface of face 12 is preferably lapped but need not be highlypolished. A satin or etched surface will suffice. In preparing face 12,the fact that face 12 will be tightly pressed against a ceramic facemust be kept in mind. Good results have been obtained in finishingsurface 12 on a precision surface grinder using an accurately dressed,fine stone wheel. The ceramic material can resist compressive forces ofgreat magnitude. However, such ceramic materials are brittle and willcrack unless the matching surfaces are accurate. Some coining" of thesilver coating on ceramics fills in microscopic irregularities under thecompressive forces used.

Referring now to the ceramics, two discs 20 and 21 have disposed betweenthen high potential metal disc electrode 22. As is well known, ceramics20 and 21 are poled so that the appropriate faces are in the rightdirection. The polarities of the two ceramics are such that when a highelectric potential is applied across the faces of each ceramic (theceramic faces are electrically connected in parallel) the reaction ofthe ceramics are mechanically aiding so that essentially the twoceramics are in series mechanical relation. This arrangement is wellknown in the art.

High potential electrode 22 consists of a metal disc having a thicknessof the order of about 3/16 of an inch. Electrode 22 may be of anydesired electrically conducting material such as aluminum, brass, steel,etc., and has its opposite faces finished to the same degree of accuracyas end face 12 of rear metal slug 10. Electrode disc 22 is thick enoughto provide support for electrical terminal 22a to which an insulatedelectrical conductor may be connected. The ceramic assembly, includingceramics 20 and 21 and intervening electrode 22 have the same outer andinner diameters. The inner diameter of the parts making up the ceramicassembly is preferably somewhat larger than the diameter of bore 14 ofrear slug 10 to accommodate tubular insulator 25, disposed between theinner surfaces of the ceramics and electrode on the one hand and outersurface of bolt 27 passing through rear slug 10 and within insulator 25.Insulator 25 is made of material which is a good electrical insulatorand can withstand a reasonable degree of heat and ultrasonic vibration.As an example, insulator tube 25 may be of teflon or silicone rubber orfiberglass. Each of these insulating materials can withstandtemperatures of the order of about 500 F. Buna N and Neoprene rubber mayalso be used in lower power units.

Ceramics now available can withstand temperatures of about 400 500 F.without'undue depolarization. The potentials used on ceramics arenormally of the order of four or five hundred volts for this type ofstructure. As a rule the dielectric constant of the insulator is notimportant since the operating frequencies, usually about 2OKHz, are toolow to result in dielectric losses of any magnitude.

Bolt 27 is threaded along as much of the bolt length as necessary toinsure a firm grip with the internally threaded part of, in thisinstance, a front horn.

Bolt 27 must have an overall length such that the bolt head at one endand threaded portion at the other end are well spaced from the ceramicassembly and the nodal plane region beyond ceramic 21, to be describedlater. When a transducer assembly is ready for operation, bolt 27 has astatic tension which is uniform along the bolt length. In transduceroperation, dynamic conditions in the transducer result in superimposingon bolt 27 added tensile forces which may increase or decrease thenormal bolt static tension. (It is understood that bolt 27 should nothave its tension reduced to zero at any time.) When bolt 27 is subjectto dynamic loading, it is stressed to maximum values along its lengthand near the transducer nodal plane and should have maximum metal toresist tension. Hence it is desirable to have the threaded bolt partwell spaced as pointed out. The threaded bolt part however must be longenough so that a strong coupling through the bolt threads can beprovided. As an example for the dimensions of ceramics given, thethreading should. be about one-half or three-fourths inches long.

Bolt 27 fits loosely within smooth bore 14 of rear slug l and the bolthas head 29 dimensioned to fit within bore 15 of slug 10. Bolt head 29is generally of the internally wrenching type as the so-called Allentype having a recessed hex so that a hexagonal rod may be used to torqueup the bolt. As is usual in this art, bolt 27 may be of high strengthsteel, or other'fatigue resistant materials, which can withstand a hightensile force used for compressing crystals and 21.

As previously set forth, bolt 27 is maintained in tension to apredetermined value, about which value dynamic conditions incident toacoustic transducer operation result in transient increase or decreaseof static bolt tension. It is desirable that the static tensionoperating point be maintained at a constant value over variations intemperature which might result in variations of bolt length. Conicalspring washers (Belleville) are provided for this purpose and forconvenience, one or more such washers are disposed between the boltheadand shoulder 16 created by counterbore 15 at the inner end thereof. Ifmore than one such conical spring washer is used, they may be arrangedin any desired fashion (large end opposed; small ends opposed) dependingupon washer characteristics. Such use of conical spring washer orwashers maintains a substantially constant bolt tension for staticconditions in spite of ambient temperature conditions.

Referring to tubular insulation 25, it is desirable that this fit assnugly as possible to the inner surfaces of ceramicsj20 and 21 andelectrode 22. Insofar as bolt 27 is concerned, it is selected to be of alength and having elastic properties consistent with engineeringrequirements involved in tensioning the bolt to obtain the desiredamount of compression upon the ceramic assembly. It is also desirable tohave the diameter of bolt 27 as small as possible and the diameter 'ofhead 29 as small as possible. While the tension in bolt 27 serves tocompress ceramics 20 and 21 on opposite sides of high potentialelectrode 22, bolt 27 essentially is a foreign but very necessaryelement. Care must be taken to avoid excessive bolt length so that theresonant frequency of the bolt is not too close to the resonantfrequency of the transducerassembly. This will minimize the interferencebetween the acoustic energy of the transducer proper and acoustic energywithin 'bolt27. Bolted tightly to the threaded end portion of bolt 27 isforward horn 30 of suitable metal such as hard alumithe same degree asface 12 of rear slug 10. Bolt 27 has.

an unthreaded part of its length extending forwardly of rear horn face31 in a counter-bored rear portion of horn recess 34. The threaded endportion of bolt 27 engages the blind threaded end portion of horn 30 topermit horn 30 to be tightened on bolt 27 enough to tension bolt 27 to aprescribed value for compressing the ceramics.

In assembling the transducer, it is preferred to dispose the rear slug,ceramics, including the high potential electrode, and horn in jigs tokeep them in desired relative position while restraining them againstrelative rotation to minimize torsional effects in ceramics. The boltand conical washer (or washers) are then disposed in proper position andthe bolt head is then turned to create the desired bolt tension. 1

Front member 30 as illustrated in FIG. 1, is ahorn whose small forwardend mayfunction as a tool or may actually carry a tool for applyingacoustic energy to a load. Such a horn construction, insofar as itsforward end is concerned, is conventional.

Instead of horn 30, a cylindrical slug 30' shown in dotted outline, maybe used. Slug 30' will require the addition of suitable tool members.Slug 30 will usually be shorter than horn 30. No attempt has been madeto show parts to scale. In all instances, the rear part of the frontmember (horn or slug) will always have a cylindrical portion 31. If slug30 is used, it may be desirable to have a bore through the entire sluglength or have a threaded recess at the forward end of the slug,generally similar to FIG. 5 extending forwardly of rear face 31 andcarrying flange 38 integral with member'30or 30'. The-overall length ofthe rear slug and ceramic assembly on the one hand and length of frontmember 30 (or 30') on the other hand are such that the nodal plane islocated at flange 38, preferably the mid plane of flange 38,perpendicular to the transducer axis. This means that front member 30(or 30') will have an overi all length greater than one fourth of a wavelength,

since that portion of the front member between rear end face 31 and halfof the flange thickness will constitute part of the rear one fourth wavelength of the transducer system. S t

Flange 38 preferably has a rectangular cross section providing sidewalls 39 and 40 and peripheral outer wall 41. Flange 38 has a thicknessalong the length of member 30 which is small in terms of operating wavelength but thick enough to be strong. Side walls 39 and 40 have curvedfillets 39a and 40a where the metal runs into the body of member 30. Asan example, the transducer so far described may have flange 38 aboutl/32 of an inchin thickness. The width radially of flange 38 may be anydesired value and theoretically this flange could extend outwardly foran indefinite distance. This is because-the nodal plane is locatedbetween side walls 39 and 40 of this flange and thus the metal at ornear the nodal plane has substantially no longitudinal movement. Forshort distances away from the nodal plane the amount of longitudinalmovement may be considered to be negligible. Consistent with mechanicalsupport requirements, the thickness of flange 38 should be a minimum.

The entire transducer assembly is supported on opposite sides of flange38 by rings 45 and 46 of strong, rigid material, such as aluminum. For.the most part,

, rings and 46 are alike, each'havingbody portion 50 and inner grippingor clamping portion 51. Forconvenience, body portion 50 is ring shapedwith outer circular edge 52. The thickness of each ring may vary and asan example, for the transducer described, the thickness of each ring maybe about five thirty seconds of an inch. The radial dimension of eachring (the difference between the inner and outer ring edges) may alsovary widely and will depend upon mechanical considerations. As anexample, the distance between the inner and outer ring edges may beabout one-half inch. Each ring has outer face 53 and inner face 54, thetwo rings normally being clamped tightly with inner faces 54 being incontact with each other.

To maintain rings 45 and 46 in tightly abutting faceto-face relation,one of the rings, as 45 for example, has its body portion 50 providedwith counter-sunk holes 56 and theother ring has threaded holes 57,which register with counter-sunk holes 56 to accommodate screws 58. Asillustrated herein four such registering sets of holes equally spacedaround body 50 of each of the two rings is provided. The remainder ofbody 50 of each of the rings has closely spaced registering holes 59 topermit air to pass through from one side of the two rings to the otherside thereof. As will be explained later, the entire transducer may bemounted within a housing and rings 45 and 46, in the absence of holes59, would impede movement of air along the length of the transducerassembly.

The diameters of holes 59 and the spacing between adjacent holes are notcritical. Instead of holes through the body of the two rings, the outeredges of the two rings as assembled may be scalloped to promote thepassage of air through or past the rings. The two rings are preferablymade of aluminum, although brass, steel or other material as non-metalmay be used.

The construction of clamping inner portion 51 of each ring will now bedescribed. Rings 45 and 46 may have identical inner clamping portions.The inside surface of clamping portion 51 of each ringhas a series offlat steps. Beginning with inner face 54 of each ring, first step 61 hasthe maximum diameter and is large enough to clear by a small fraction ofan inch outer surface 41 of flange 38. The axial dimension of each step61 is more than one half the thickness between flange side walls 39 and40 as suggested in FIG. 4, sufficiently so that ring metal and flangemetal will never touch. When two rings are clamped together tightly,both steps 61 cooperate to encircle outer wall 41 of flange 38 having anannular clearance such as about fifteen thousandths of an inch for theexample given. Next step 62 is dimensioned to engage the outer surfaceof O-ring gasket 63 having a rectangular cross section. Each clampingring 45 and 46 cooperates with each of the two O-rings 63. Ring 63 is ofcompressible or deformable material which can withstand substantial heatand will not break down from acoustic energy. As an example, suchmaterials as silicone rubber, Teflon, Buna-N and neoprene rubbers may beused. The normal cross section of gaskets 63 is preferably rectangularand dimensions are such that when the parts are assembled, adequatecompression results with substantially full contact between gasketsurfaces and metal established. It is possible to use O-rings ofcircular section and correspondingly shape the surfaces engaging thegasket.

It is important that relative rotary movement between the transducerproper and its mounting be prevented. Such movement might be at thesurfaces of metal and material of gaskets 63. Rotary movement therecould result in broken wire leads. To avoid such movement, it ispossible to interlock the gasket material and metal pressed against suchgasket material.

Thus side walls 39 and 40 of flange 38 could have inbe locked againstrotary movement when the transducer is assembled. The O-ring gaskets maybe positioned on each flange side at an appropriate time, whenassembling, and cemented if desired.

The compression of the gasket material should be limited to avoidincreasing conductivity of gasket material to acoustic energy to anundesirably high level. So long as the gasket material is soft enough topermit relative play of the transducer and the mounting, the gaskets,particularly in view of their proximity to the nodal plane, willessentially isolate the transducer from acoustic energy leakage at themounting and prevent destruction of the mounting system.

Step 65 is at the outer face 53 of each ring and has the minimum insidediameter for each mounting ring. Gaskets 63 are normally quite soft (forexample a Durometer value of about 50 may be used) but compression issufficient to makethe suspension stiff enough to be workable. In anyevent, clearances and suspension stiffness are such that any acousticcoupling from the transducer to the mounting ring is via the gasketsonly.

For a transducer operating at approximately 20 KHz, a 1% inch diametersteel rear slug may have an overall length of about 1% inches, a forwardaluminum 1% inch slug may have an overall length of about 2% inches, twoceramics each about one-fourth inch thick and a high potential electrodeabout 7/32 inches thick may make up a trasducer having a half wavelength of a bit over 4% inches. It is understood of course that thedimensions may vary with design parameters. The nodal plane will bepredetermined to be at the flange mid section near the rear of theforward member.

Instead of having a forward horn130 carry a tool at end 132, as shown inFIG. 5, it is possible to add a resonant extension of proper material,proper length and suitable acoustic impedance characteristics.

The front member 30 (or 30) illustrated in FIG. 1, has flange 38 spacedaway from end face 31 by substantially the thickness of a gasket. Thisenables both gaskets to be positioned accurately on opposite sides offlange 38 on the same member prior to assembling clamping rings 45 and46.

It is possible, however, to have flange 38 at the rear end of theforward member so that a flange side wall is part of end face 31. Thisis illustrated in FIGS. 5 and 6 which show a front member 130. In thisfront member, the rear end portion of member 130 will be cylindrical,even though the remainder thereof may have any desired shape. One gasketring will overlie the cylindrical portion of member 130 forwardly offlange 38 while the companion gasket ring will be disposed about theforward cylindrical end of the ceramic part 21 of the system. When theouter clamping rings are applied to each of the two gaskets in the formjust described, it is possible that one gasket may tend to be eccentricwith respect to the other gasket so that somewhat greater care inassembling the entire structure may be required.

A housing for a transducer assembly will generally be a practicalnecessity over the rear portion of the transducer beginning with themounting rings and extending rearwardly over the ceramics, highpotential electrode and rear slug. A simple housing of generallycylindrical construction may be provided. Housing 70 may either be ofsynthetic material as plastic or may be of metal such as aluminum ofsufficiently heavy gauge to withstand rough use. While a housing may becylindrical, there is no particular necessity for such a shape and,instead, the housing may have a rectangular cross section. This, ofcourse, would require a different shape for the outer edges of themounting rings or might require some adapter between the inside surfaceof the housing and the outer portion of the mounting rings.

A simple mounting for a transducer within housing 70 may have aninwardly extending shoulder 71. The inside diameter of housing 70 may belarge enough to accommodate the outer edge of the mounting rings whileinner shoulder 71 would provide a support against which the mountingrings may be disposed and to which they could be attached. As anexample, inner shoulders 71 may be of aluminum and have a series ofholes registering with the holes in the mounting rings. Retaining boltsmay be used at a number of such holes to attach the mounting rings tothe housing shoulder. Any other attaching means between housing 70 andthe mounting rings of a transducer may be used.

It may be desirable to provide a blast of cooling air for dissipatingany heat generated by the transducer unit. The direction of flow of sucha glast of air is preferably rearwardly of the transducer beginningabout at the mounting rings and extending within the housing past therear free end of the transducer. By having the blast of air travel inthat direction, there will be less likelihood of air blasts on the workwith consequent blowing of fine particles. The air blast itself may beprovided in a number of ways as for example by fan 74 driven by electricmotor 75 supported within the housing. It is understood, of course, thatthe rear end of the housing will be open to the atmosphere so that acontinuous blast of air may travel through the holes in the mountingrings and over the exposed surfaces of the ceramics, high potentialelectrode and rear slug.

Suitable wire leads for the electric motor, the grounded rear slug,forward member or whatever metal parts are used forwardly, mountingrings and housing, if of metal, are disposed within the housing. A leadfrom the high potential electrode and a ground wire from the mountingring (if such mounting rings are electrically insulated from the housinginterior as would be the case in a housing of plastic material) must becarefully located on the transducer as close to the nodal plane aspossible. Precautions conventional in this art to prevent crystalizationof wire are followed.

The mounting of a transducer may, in some instances, require somedifferences in the mechanical construction of the mounting rings. Forexample, rings 45 and 46 are circularly continuous. However, it ispossible to have a mounting ring assembly where a ring is divided intotwo semi-circular portions each of which essentially integrates halfring 1460 and half ring l46b to extend over the edge of flange 38. Thetwo semicircular ring portions may be bolted together by overlappingextensions as illustrated in FIG. 8. In certain instances it may bedesirable to have one of the mounting rings the one nearest to the outersurface of the ceramic circularly continuous and have a cooperating'ring divided into two semicircular parts. Such an arrangement isrequired for a horn shown .in FIG. 7, where the metal forwardly offlange 38 is outwardly expanding so that a continuous ring cannot beused. In such instances, a onepiece ring may be used on one side of theflange and a composite split ring may be positioned on the other side ofthe flange. The gaskets have sufficient elasticity to be stretched overa flange.

Referring specifically to FIG. 8, one mounting ring, in this case 45, iscircumferentially continuous and is provided with suitable holes throughthe ring. This solid ring has a stepped interior generally similar tothe stepped interior of one of the two rings illustrated in FIGS. 3v and4. Solid ring 45 is adapted to go about the cylindrical end of a hornsuch as, for example, shown in FIG. 7 on the side of the flange nearestthe small end face of the horn.

Split ring 146 has portions 146a and 146b which provide generallysemi-circular rear portions. At the split, the ring ends are stepped asshown so that two semicircular rings may be fitted to make a completering. It is clear that the split ring may be disposed about the narrowannular cylindrical surface of the horn adjacent the flange but locatedon the far side of said flange away from rear end of the horn. Bescrewing or bolting the various parts or the ring portions together, theentire mounting assembly for a horn, such as illustrated in FIG. 7, maybe provided to accommodate an outwardly flaring horn surface.

Other ring splitting procedures may be adopted to permit mounting of atransducer assembly for work.

It will be clear that the invention provides a transducer assembly whoselateral mounting space requirements are minimized. Thus, a transducerassembly of the type illustrated in the drawing (with or without thehousing as desired) may be disposed inclose proximity to similartransducers. The only clearance between adjacent transducers is normallydetermined by the radial extension of the flange beyond the outersurfaces of the transducer. Such economy of mounting space permits ofclose disposition and operation of a plurality of transducers. Noattempt is made to show relative proportions of radial dimensions of atransducer mounting flange and the transducer proper. It is obvious thata number of transducers can be mounted side by side on a plate and soclosely spaced that the outer flange diameters nearly touch.

It is possible to remove flange portions between adjacent transducers topermit closer transducer spacing of a cluster of transducers. Thus,instead of a 360 continuous flange mounting, cutouts of metal and gasketportions over small arcuate regions about a transducer permit minimumspacing between transducers for maximum application of acoustic energyat a given locale.

I claim:

1. An ultrasonic transducer comprising two piezoelectric ceramic discswith a high potential electrode therebetween arranged to form a stack,said ceramic discs having flat surfaces, electrically grounded front andrear acoustic resonators axially aligned with said stack and havingconforming shapes and at least equal areas cooperating with the flatdisc surfaces, axially disposed bolt means for retaining as an assemblysaid resonators and said stack under predetermined compression, saidfront resonator having its rearend portion shaped so that sectionstransverse to the resonator axis are, circular, and the front endthereof being adapted to feed ultrasonic energy for work, said rearendportion having an integral outwardly extending uniformly thick supportflange having a thickness along the front resonator length which issmall in terms of operating wave length but thick enough to be strong,said transducer having a nodal plane at the flange; mating rigid ringsdisposed at opposite sides of said flange, a readily compressible heatresistant gasket ring at each side of said support flange, each saidgasket ring contacting substantially all of the opposed surfaces of saidflange sides and portions of said rigid rings and also contacting outersurfaces of the transducers said assembly parts adjacent the flange,means for supporting said rigid rings in predetermined spacedrelationship, said rigid rings forming part of a mount for the entiretransducer assembly, said rigid rings having sufficient clearance withrespect to the body of said transducers said assembly parts toaccommodate limited vibration isolation at said gasket rings consistentwith mounting rigidity between the transducer assembly and said rigidrings, the generally distributed compression of gasket rings betweengasket compressing surfaces preventing the formation of destructivelocalized hot spots in said gasket material; said transducer havingminimum interfaces to minimize interface losses and the flangetransmitting directly to said front resonator load pressure withoutsignificantly affecting the nature or distribution of the predeterminedcompression force on the ceramics and without increasing the bolttension significantly.

2. The construction according to claim 1 wherein said flange is locatedforwardly of the rear end face of the front resonator so that said twogasket rings may be disposed on opposite sides of the flange about therear end portion of said front resonator.

3. The construction according to claim 1 wherein at least one'of thesurfaces against which a gasket is compressed has relatively smallirregularities for frictionally locking the adjacent gasket materialagainst relative movement whereby a gasket is prevented from moving withrespect to the transducer about the axis of said transducer assembly.

4. The construction according to claim 1 wherein said flange is locatedso that one sidewall thereof forms an extension of the rear end of saidfront resonator with one gasket overlying the adjacent end of a ceramic.

5. The construction according to claim 1 wherein said front resonatortapers from its flanged rear end portion with said resonator crosssectional area decreasing as the front end is approached, said frontresonator having a length somewhat in excess of onequarter wave length,said front end of said front resonator providing a mechanical advantagein amplitude increase whereby a compact transducer structure isprovided.

1. An ultrasonic transducer comprising two piezo-electric ceramic discswith a high potential electrode therebetween arranged to form a stack,said ceramic discs having flat surfaces, electrically grounded front andrear acoustic resonators axially aligned with said stack and havingconforming shapes and at least equal areas cooperating with the flatdisc surfaces, axially disposed bolt means for retaining as an assemblysaid resonators and said stack under predetermined compression, saidfront resonator having its rear-end portion shaped so that sectionstransverse to the resonator axis are circular, and the front end thereofbeing adapted to feed ultrasonic energy for work, said rearend portionhaving an integral outwardly extending uniformly thick support flangehaving a thickness along the front resonator length which is small interms of operating wave length but thick enough to be strong, saidtransducer having a nodal plane at the flange; mating rigid ringsdisposed at opposite sides of said flange, a readily compressible heatresistant gasket ring at each side of said support flange, each saidgasket ring contacting substantially all of the opposed surfaces of saidflange sides and portions of said rigid rings and also contacting outersurfaces of the transducer''s said assembly parts adjacent the flange,means for supporting said rigid rings in predetermined spacedrelationship, said rigid rings forming part of a mount for the entiretransducer assembly, said rigid rings having sufficient clearance withrespect to the body of said transducer''s said assembly parts toaccommodate limited vibration isolation at said gasket rings consistentwith mounting rigidity between the transducer assembly and said rigidrings, the generally distributed compression of gasket rings betweengasket compressing surfaces preventing the formation of destructivelocalized hot spots in said gasket material; said transducer havingminimum interfaces to minimize interface losses and the flangetransmitting directly to said front resonator load pressure withoutsignificantly affecting the nature or distribution of the predeterminedcompression force on the ceramics and without increasing the bolttension significantly.
 2. The construction according to claim 1 whereinsaid flange is located forwardly of the rear end face of the frontresonator so that said two gasket rings may be disposed on oppositesides of the flange about the rear end portion of said front resonator.3. The construction according to claim 1 wherein at least one of thesurfaces against which a gasket is compressed has relatively smallirregularities for frictionally locking the adjacent gasket materialagainst relative movement whereby a gasket is prevented from moving withrespect to the transducer about the axis of said transducer assembly. 4.The construction according to claim 1 wherein said flange is located sothat one sidewall thereof forms an extension of the rear end of saidfront resonator with one gasket overlying the adjacent end of a ceramic.5. The construction according to claim 1 wherein said front resonatortapers from its flanged rear end portion with said resonator crosssectional area decreasing as the front end is approached, said frontresonator having a length somewhat in excess of one-quarter wave length,said front end of said front resonator providing a mechanical advantagein amplitude increase whereby a compact transducer structure isprovided.